The present invention relates to an impact dot print head, and in particular to an impact dot print head in which an electromagnetic force is used to cause the print wire to strike the platen.
Electromagnetic impact dot print heads are known in the art. One type of a conventional impact dot print head, as shown in FIG. 1, includes a core 63. A permanent magnet 62 is positioned within core 63 and an elastic arm 61 is supported on core 63 and supports a drive print wire 60. A magnetic member 65 is supported on elastic arm 61 and is attracted by permanent magnet 62, acting through the core. A conductive coil 64 is mounted about core 63 and and cancel a magnetic force produced by the permanent magnet when current flows therethrough.
Magnetic member 65 is attracted to core 63 due to the magnetic force of permanent magnet 62 thus deflecting elastic arm 61 toward core 63. This displaces print wire 60 in a direction away from the platen. To print, current is caused to flow through conductive coil 64 to provide a magnetic field which cancels the magnetic attraction between core 63 and magnetic member 65 thereby causing elastic arm 61 to drive print wire 60 towards the platen due to the restoring force of elastic arm 61.
A second conventional impact dot print head, shown in FIG. 2, includes a core 72 having an arm 68 pivotable mounted thereon. Arm 68 supports a print wire 66 at one end. A magnetic member 74 is mounted on arm 68. A conductive coil 70 is mounted on core 72 and provides a magnetic current when current flows therethrough. When in a non-printing position arm 68 contacts the inner surface of print head case 67, and is preferably held in that position by a biasing means (not shown).
Printing occurs by applying a current to solenoid 70. A magnetic field is formed attracting magnetic member 74 towards core 72 driving print wire 66 towards the platen.
Both of these conventional print heads have been satisfactory. However, they suffer from the disadvantage that they both produce a large amount of noise during operation. In the print head of FIG. 1, magnetic member 65 contacts core 63 in the non-printing position, similarly in the conventional print apparatus of FIG. 2 arm 68 contacts case 67 in the non-printing position. Accordingly, an impact noise occurs after each print stroke causing a large amount of noise during a series of successive print operations. To solve such problems, elements for absorbing the impact are provided in a position where the movable member and the non-movable member contact each other. However, these impact absorbing members are easily deformed so that the initial or preprinting position becomes changed over time, deteriorating the print quality. Furthermore, because the impact of the absorbing members can not fundamentally solve the problem, the noise generation can not be effectively controlled.
Accordingly, it is desired to provide an impact dot print head which removes the noise generated when the print wire returns to the non-print position without utilizing a deformable impact absorbing member.